United Kingdom invocation of Article 50 of the Treaty on European Union

The United Kingdom's invocation of Article 50 of the Treaty on European Union happened on 29 March 2017, and it began the United Kingdom's withdrawal from the European Union (EU), commonly referred to as Brexit. The invocation of Article 50 is the act of giving formal notice to the European Council of a member state's intention to withdraw from the EU to allow withdrawal negotiations to begin, in compliance with the Treaty on European Union.

The process of leaving the EU was initiated by a referendum held in June 2016 which favoured British withdrawal from the EU. In October 2016 the Prime Minister of the UK, Theresa May, announced that Article 50 would be invoked by "the first quarter of 2017". On 24 January 2017 the Supreme Court ruled in the Miller case by a majority that the process could not be initiated without an authorising act of parliament, and unanimously ruled against the Scottish government's claim in respect of devolution. Consequently, the European Union (Notification of Withdrawal) Act 2017 empowering the prime minister to invoke Article 50 was enacted in March 2017.

Invocation of Article 50 occurred on 29 March 2017, when Sir Tim Barrow, the Permanent Representative of the United Kingdom to the European Union, formally delivered by hand a letter signed by Prime Minister Theresa May to Donald Tusk, the President of the European Council in Brussels. The letter also contained the United Kingdom's intention to withdraw from the European Atomic Energy Community (EAEC or Euratom). This means that the UK will cease to be a member of the EU on 30 March 2019, unless an extension to negotiations is agreed upon by the UK and EU.

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